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Frequent Contributor

VRRP the preempt is enabled by default

Hi Guys

in VRRP  the preempt is enabled by default ,so shall we disable on the backup device , what mess we got if  we didn't disable prempt on the backup

thanks  

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Hall of Fame Cisco Employee

Ibrahim,

Ibrahim,

There are no significant drawbacks to having preemption activated. In fact, I would recommend keeping it activated at all times on all VRRP routers. It helps to keep the Master role deterministic: It will always be the router having the highest momentary priority. Without the preemption, the choice of the Master role would be a matter of chance, and most importantly, if you used some kind tracking (such as uplink interface tracking), the Master role would not be passed over to the other router whose uplink is still working.

Best regards,
Peter

Highlighted
Frequent Contributor

Hi

Hi

I was asking if we keep it active on the backup , on the master it must be there , i am asking what would happend if we keep it on the the backup

pls clarify

thanks 

Highlighted
Hall of Fame Expert

Hello Ibrahim,

Hello Ibrahim,

in Peter's post is implicit that preemption should be kept active on both the master and the backup routers for the good reasons he has explained.

You need the preemeption also in the backup in order to make it able to take over if a topology change makes its VRRP priority better than that of the current master.

This will cause a change of master, but it is wanted by design of the VRRP protocol.

It is not enough to have the preeempt on the current master router.

Hope to help

Giuseppe

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Frequent Contributor

Hello bro Giuseppe Larosa

Hello bro Giuseppe Larosa

i have question , , which of the below is correct config on Cisco Nexus with PVST+ or rapid pvst  to make N7K-1 root primary  for all vlan while N7K-2 the root sec for all VLANs

N7K-1

spanning-tree vlan 1-4093 root primary

N7K-2

spanning-tree vlan 1-4093 root secondary

or or 

N7K-1

spanning-tree vlan 1-3967 root primary

N7K-2

spanning-tree vlan 1-3967 root secondary

thanks 

Highlighted
Beginner

Don't pay attention, some

Don't pay attention, some people can't explain properly for all type of peoples. 

VRRP is slighlty different than HSRP, first of all because it can use many Backups Routers (Standby in HSRP) and the second is that VRRP has the preemption enabled by default. When the Master fails, the Backup Router can take over the role if it has that preemption enabled, if it doesn't, it will not take the role of Master from the failed Master, so we need Preemption enabled in order to make that work.

HSRP is much more simpler with Preemption I would say, you just gotta specify on the Active Router the priority and enable preemption with the "hsrp 1 preempt" command and that's it, you said to the Router to take back his role if it fails and then comes back up. But for the Standby Router we don't need to worry about preemption, because it will take over the Active role of the failed Active Router.

Best regards, 

Stefan Timuta

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